feat(plugins): add JSON parsing/serialization (#6420)

Reviewed-by: Mm2PL <mm2pl+gh@kotmisia.pl>
Reviewed-by: pajlada <rasmus.karlsson@pajlada.com>

docs/lua-meta/json.lua

@@ -0,0 +1,28 @@
+---@meta chatterino.json
+
+local json = {}
+
+--- Parse a string as JSON
+---
+---@param input string The text to parse
+---@param opts? {allow_comments?: boolean, allow_trailing_commas?: boolean} Additional options for parsing. `allow_comments` will allow C++ style comments (`[1] // text`). `allow_trailing_commas` will allow commas before an object/array ends (`[1, 2,]`).
+---@return any
+function json.parse(input, opts) end
+
+--- Stringify a Lua value as JSON. Only tables and scalars (strings/numbers/booleans) are supported.
+--- Empty tables are stringified as objects. To get an empty array, use the following: `{ [0] = json.null }` (will produce `[]`).
+--- Tables with `nil` values like `{ foo = nil }` will be stringified as `{}` (they are identical to the empty table). To get `null` there,
+--- use `json.null`: `{ foo = json.null }` (produces `{"foo":null}`).
+---
+---@param input any The value to stringify
+---@param opts? {pretty?: boolean, indent_char?: string, indent_size?: number} Additional options for stringifying. The default pretty indent char is a space and the size is 4.
+---@return string
+function json.stringify(input, opts) end
+
+---Helper type to indicate a `null` value when serializing.
+---This is useful if `nil` would hide the value (such as in tables).
+---See `json.stringify` for more info.
+---@type lightuserdata
+json.null = {}
+
+return json